The overall goal of the proposed research is to assess the role of IGF-IR gene expression in normal renal development and its contribution to disorders of kidney development such as Wilms tumor. The product of WT1, the Wilms tumor suppressor gene, is a zinc-finger transcription factor that generally represses its target genes. WT-1 expression is necessary for normal kidney development and mutation or loss of the WT-1 locus is often associated with Wilms tumor. The investigator has proposed previously that WT-1 regulation of the IGF-IR gene is an important factor in metanephrogenic development, and that alterations in this control mechanism result in aberrant kidney development. The investigator now proposes to examine mechanisms involved in regulation of IGF-IR expression by WT-1. The main hypothesis to be tested will be that various isoforms of WT-1 control IGF-IR gene expression through differential binding and protein-protein interactions with other transcription factors. Four Specific Aims are proposed. 1) To demonstrate regulation of endogenous IGF-IR gene expression in 293 human embryonic kidney cells by modulation of endogenous WT-1 gene expression and/or WT-1 action. 2) To assess the effects of naturally occurring and clinically relevant mutant forms of WT-1 on regulation of IGF-IR gene expression in a kidney derived cell line that lacks WT-1. 3) To investigate the interaction of WT-1 proteins with the transcriptional activator Sp-1, which is required for basal IGF-IR promoter activity, and which may be a necessary component for WT-1 mediated repression of IGF-IR gene expression. 4) To identify other proteins that may interact with WT-1 and contribute to its activity; these may include other transcription factors or proteins that modify WT-1 structure.